Add full test suite with pytest

tests/test_cli_helpers.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from chguard.cli import (
+    _common_snapshot_root,
+    _extract_paths_from_command,
+    _parse_prune_states_value,
+)
+
+
+def test_parse_prune_states_value_accepts_days_and_all(monkeypatch) -> None:
+    assert _parse_prune_states_value("14") == 14
+    assert _parse_prune_states_value(" all ") == "all"
+
+    monkeypatch.setenv("CHGUARD_STATES_LIFE", "30")
+    assert _parse_prune_states_value(None) == 30
+
+
+@pytest.mark.parametrize("value", ["", "abc", "-1"])
+def test_parse_prune_states_value_rejects_invalid_values(
+    value: str, monkeypatch
+) -> None:
+    monkeypatch.delenv("CHGUARD_STATES_LIFE", raising=False)
+
+    with pytest.raises(SystemExit):
+        _parse_prune_states_value(value)
+
+
+def test_extract_paths_from_command_returns_existing_non_options(
+    tmp_path: Path, monkeypatch
+) -> None:
+    monkeypatch.chdir(tmp_path)
+    target = tmp_path / "file.txt"
+    target.write_text("data", encoding="utf-8")
+
+    paths = _extract_paths_from_command(
+        ["chmod", "-R", "644", "file.txt", "missing.txt"]
+    )
+
+    assert paths == [target.resolve()]
+
+
+def test_common_snapshot_root_uses_single_path_or_common_parent(
+    tmp_path: Path,
+) -> None:
+    one = tmp_path / "one"
+    two = tmp_path / "two"
+    one.mkdir()
+    two.mkdir()
+
+    assert _common_snapshot_root([one]) == one.resolve()
+    assert _common_snapshot_root([one, two]) == tmp_path.resolve()